#1 Cuban Underwater City
This is another underwater site that in fact is raising more questions than providing answers. According to scientists, it would take approximately 50,000 years for this kind of city to be submerged to its current depth. The ruins represent corridors and buildings, including huge granite complexes and pyramids. So until the site is better studied, it is very difficult to say what exactly it is, but the possibility of it being a lost ancient city still remains.